Reduction of radioactive gas contamination of nuclear detonations in geological formations

ABSTRACT

Oxidizing agents are disposed circumjacent to a nuclear explosive device detonated in a geological formation, generally a carbonaceous or petroliferous formation, to provide a more oxidizing environment thereabout. Upon detonation of the device reductants present in the formation as well as in emplacement components are oxidized. Consequently tritium produced by the detonation together with any hydrogen gas present tends to be oxidized to form a tritiated water product. The water combines with inorganic materials in the vicinity of the detonation and is immobilized or falls to the bottom of the detonation produced cavity so as to minimize the tritium content of organic materials evolved by the formation.

United States Patent Heckman et al.

[151 3,703,208 51 Nov. 21, 1972 [72] Inventors: Richard A. Heckman,Castro Valley; John O. Cowles, Livermore, both of Calif.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission [22] Filed: Jan. 22, 1971 [21] Appl.No.:108,976

[52] U.S. Cl ..166/247 [51] Int. Cl. ..E2lb 43/00 [58] Field of Search..l66/247, 63

[56] References Cited UNITED STATES PATENTS 3,608,636 9/1971 Dixon166/247 OTHER PUBLICATIONS A-Blast Set for Peace Use Test, Nov. 12,1958,

Washington Post and Times Herald Frank W. Stead, Tritium Distribution inGround Water Around Large Underground Fusion Explosions, Nov. 1963, pp.1163-1165, Science, Vol. 142.

World Oil, September 1969, Project Pulison, pp. 67-71 PrimaryExaminerRobert L. Wolfe Attorney-Roland A. Anderson [57] ABSTRACTOxidizing agents are disposed circumjacent to a nuclear explosive devicedetonated in a geological formation, generally a carbonaceous orpetroliferous formation, to provide a more oxidizing environmentthereabout. Upon detonation of the device reductants present in theformation as well as in emplacement components are oxidized.Consequently tritium produced by the detonation together with anyhydrogen gas present tends to be oxidized to form a tritiated waterproduct. The water combines with inorganic materials in the vicinity ofthe detonation and is immobilized or falls to the bottom of thedetonation produced cavity so as to minimize the tritium content oforganic materials evolved by the formation.

7 Claims, No Drawings REDUCTION OF RADIOACTIVE GAS CONTAMINATION OFNUCLEAR DETONATIONS IN GEOLOGICAL FORMATIONS BACKGROUND OF THE INVENTIONIn utilizing nuclear detonations for various un- 0 derground engineeringapplications a major concern is the possible release or venting ofradioactive products to the surface environment. It has generally beenconsidered that most of the radioactive products produced in suchdetonations would be trapped as non-volatile or insoluble constituentsin solidified melt zone material produced in the formation in thevicinity of the detonated device. The immobilization of such radioactiveproducts does appearto occur in many applications with detonationsconducted in certain formations. However, in many other cases, gaseousradioactive products appear in undesirable or hazardous amounts as acontaminant in fluid and gaseous materials evolved or transportedthrough the chimney created in the formation by the detonation.

Contamination of fluid and especially of gaseous hydrocarbons by tritiumproduced in such detonations is of particular concern where nucleardetonations are to he used for stimulating production of gaseous andfluidic hydrocarbons from petroliferous formations. Domestic reserves ofnatural gas in known deposits having permcabilities and othercharacteristics permitting economically feasible production are rapidlybecoming inadequate to supply ever increasing demands. Very largereserves of natural gas and other petroleum hydrocarbons exist informations of great thicknesses which either have too low a permeabilityfor economic production by conventional techniques or which contain thehydrocarbon in a form not recoverable by conventional methods. Variousmethods have been proposed wherein nuclear explosives are detonated insuch formations to increase the effective permeability or to otherwiseprepare the formation for hydrocarbon recovery. Two nuclear detonationexperiments, i.e., Gasbuggy and Rulison have been conducted in thick,low-permeability (tight) hydrocarbon reservoirs with a consequentstimulation of natural gas production as disclosed, for example, in"Proceedings of the Symposium on Engineering with NuclearExplosives"Jan. l4-l6, 1970, Las Vegas, Ncv., issued May 1970. When anuclear explosive is detonated in such a formation as well as incertainother underground nuclear detonation environments, there is firstproduced a generally spherical chamber including a large amount ofmelted material which may temporarily line the chamber and portions ofwhich may thereafter form a puddle in the lower portion of the chamber.Later, the upper portion of the chamber may cave progressively forming achimney in the formation which chamber together with the chimney and theassociated fracture system comprise the principal means whereby theformation permeability is increased. The melted formation portions areoften termed the melt" zone which on cooling and solidifcation forms arather insoluble vitreous or glass-like substance in which radioactivedetonation products are to a large extent trapped.

ln usual practice it has been considered that fission yield devices maybe used in preference to fusion devices to minimize tritium generated inthe device itself; however, this would increase the cost of theexplosive and, even with pure fission explosives, significant amounts oftritium are produced by neutrons emanating therefrom and interactinggenerally with lithium present in the rock. The tritium which isproduced is, of course, in a gaseous state and intermixes with the gasesformed in the detonation and thereafter with natural gas, fluidhydrocarbons, or water which enter the chimney from the formation, e.g.,during product withdrawal. Moreover, the tritium can undergo exchangereactions with the hydrogen of the gaseous or fluid hydrocarbonsproviding tritiated compounds which together with the gaseous tritiumcannot be easily or economically separated from such hydrocarbons. Thetritium gas and tritiated gas content creates a hazard, e.g., when thehydrocarbons are burned especially in household devices since thetritiated water produced can be inhaled to enter the body. Accordingly,it is readily apparent that a need exists by which tritium contaminationof products including gaseous and fluidic hydrocarbons extracted fromnuclear detonation environments can be minimized.

SUMMARY OF THE INVENTION The invention relates, generally, to proceduresfor reducing radioactive contamination of fluid and gaseous materials byunderground nuclear detonations and, more particularly, to a procedurefor minimizing contamination of fluid and gaseous hydrocarbons bytritium produced incident to detonation of a nuclear explosive in apetroliferous formation.

Tritium contamination can arise in the vicinity of a nuclear explosivedevice detonated in a geological formation from several sources. Withpure fission devices excess neutrons emanating from the device caninduce reactions with lithium in the formation to produce tritium. Withother types of nuclear explosives, e.g., conventional fission-fusiondevices even more tritium can originate from the components of thedevice and from the high energy, i.e., l4 Mev neutrons produced thereininteracting with lithium and boron nuclei which are present in at leasttrace amounts in most geological formations. The amount of tritiumproduced accordingly depends upon the type of nuclear explosiveemployed, the yield of the explosive and the content of fertilematerials in the formation which may react with neutrons to producetritium. The tritium from-whatever source is generally in an atomicstate which may combine with hydrogen to form HT molecules or withorganic hydrocarbons by abstraction reactions to form tritiated gaseousor fluid hydrocarbons, thereby contaminating in situ materials. If thegaseous portions of the chimney contents should vent to the atmosphereor if the products, e.g., gaseous hydrocarbons are withdrawn for use asfor fuel, the tritium may present a serious hazard to humans and to theecological system.

Based on various observations and studies it is now considered thattritium in a gaseous contaminating state is produced where conditionsare such that a high temperature chemically reducing environment isprovided particularly in the melted zone surrounding the shot locationin the chamber produced by the detonation. Reducing conditions in thegas phase may arise from the products of reactions of naturallyoccurring materials such as water, with materials such as iron and/orother metals used in emplacement casings and canisters, plasticcomponents, etc. Materials which can function as reducing agents such ashydrocarbons and especially free carbon or carbon compounds having ahigh ratio of carbon to hydrogen, e.g., bituminous shale, coal, kerogen,etc., may exist in the formation itself. lt will be appreciated that thelatter conditions will often prevail in petroliferous formations fromwhich it may be desired to produce or extract gaseous and fluidichydrocarbon products.

Generally speaking the present invention relates to a technique whereinreagents which provide an oxidizing environment in at least the meltzone created by the detonation are disposed in proximity to andpreferably surrounding the device during emplacement. It is generallypreferred to utilize a minimum of components and materials which wouldcreate or augment a chemically reducing effect in the construction ofemplacement components, drill casing, etc. It is also contemplated thatemplacement may often be made in particular interbedded strata of theformation in which minimum amounts of reducing agent components orincreased proportions of oxidizing components are present so as tominimize the quantity of oxidizing agent required to effectively entrapthe radioactive contaminants.

With such an arrangement, on detonation of the nuclear explosive, theoxidizing agents are heated to a high temperature to melt and intimatelyintermix with at least the portions of the formations which aresimultancously melted by the detonation to provide a quantity ofoxidizing agent therein. The oxidizing agents accordingly react withreductants present therein as well as with a major portion of thetritium produced in the rock surrounding the device and/or which isreleased from the device to produce condensible products such astritiated water (HTO) molecules. The tritiated water molecules alongwith other water produced by combustion or released from the formationon heating then will partially combine with various constituents of theformation as water of hydration, e.g., in silicates, as water ofcrystallization, or to formhydrous oxides, hydroxides and otherwise tobe incorporated into solid substances in the detonation chamber therebybeing effectively immobilized therein. In this form it may be noted thatthe tritium cannot readily undergo exchange reactions with the fluid andparticularly with gaseous hydrocarbons present in the detonationchamber. Sufficient quantities of the oxidizing agent are incorporatedto assure that the various reaction equilibria are driven to anoxidative state where little or no gaseous tritium isotope remains inthe gas phase in the chamber. Whatever water vapor containing l-lTOwhich is not effectively absorbed or incorporated by solid substances inthe chamber and is entrained in the gaseous or fluid hydrocarbonswithdrawn from the chamber may be removed at the surface or byconventional drying operations such as by condensation, dehydration,etc., to further decontaminate the products.

Accordingly, it is an object of the invention to provide a method bywhich radioactive contamination of in situ gaseous and fluid products bya subterranean nuclear explosive detonation is minimized or prevented.

Another object of the invention is to provide a process wherein anuclear detonation in a geological formation is conducted in achemically oxidizing environment to minimize contamination ofextractable fluid and gaseous materials with radioactive substances.

Still another object of the invention is to provide a process wherein anuclear explosive device is emplaced in a subterranean petroliferousformation and oxidizing reagents are disposed in proximity or insurrounding relation thereto so that on detonation of the device anoxidizing environment is provided at least in the chamber and meltedrock zone formed by the detonation so that radioactive contaminantsincluding at least tritium are converted to an oxidized form which canbe entrapped by solids in the detonation chamber or which are in aneconomically removable form in gaseous materials therein.

Other objects and advantageous features of the invention will beapparent in the following description of the invention.

DESCRIPTION OF THE INVENTION It is considered that the process of theinvention may generally be applied in locales having an excess ofreducing agents comprising materials in the geological formation andemplacement components formed of chemically reducing materials such asiron and hydrogenous materials from which gaseous hydrogen orhydrocarbons may evolve. However, for illustrative purposes the processof the invention will be described as applied to nuclear detonationsconducted in a typical, low-permeability petroliferous formation orreservoir for stimulating production. of organic hydrocarbons therefrom.Domestic deposits as well as known foreign deposits occur in areascovering tens of thousands of square miles and may include severalthousand feet of continuous or contiguously interbedded stratacontaining, for example, significant quantities of natural gas in smallpoorly interconnected pores. These strata generally are sedimentary innature and comprise varying proportions of sands, clay, carbonate rockssuch as limestone and dolomite, minerals such as Fe fl limonite, tarryor coal like particles of low hydrogen to carbon ratio hydrocarbons,fluid hydrocarbons and other materials in addition to methane and othergaseous hydrocarbons.

For emplacing a nuclear explosive in such a formation, to provide adetonation effective to stimulate production therefrom, a cased oruncased borehole as appropriate may be constructed as in conventionalpetroleum production practice or as in underground nuclear testing,i.e., in the manner utilized in Gasbuggy" and Rulison natural gasstimulation experiments disclosed in the aforesaid Proceedingssee also,Emplacement and Stemming of Nuclear Explosives for PlowshareApplications .l. L. Cramer, pp. 974, of the above-referencedProceedings. Other emplacement methods may also be used, e.g., by meansof mine shaft or horizontal borehole in shallow petroliferous depositsparticularly where gas pressure may be low or non-existent.

To accommodate the required amounts of oxidants the site at which theexplosive device is to be emplaced may be enlarged as by reaming oroverboring, by using a conventional explosive camoufletting technique orother effective bore enlarging technique as appropriate under thecircumstances. It is preferred that the site of the emplaced explosivebe selected to be in a stratum having a minimum content of reducingmaterials, e.g., barren sand, clayey sandstone, clay bed or the likewhich may be interbedded, e.g., as a lens between or adjacent to thehydrocarbon strata from which production is to be stimulated. Theemplacement well may be drilled somewhat deeper than the level ofemplacement and solid, e.g., granular oxidant disposed thereinpreferably as near the explosive device as possible but not at adistance which exceeds the expected detonation chamber radius. Thenuclear device disposed in the usual emplacement canister with attachedcontrol cable and supporting means may then be lowered and positioned atthe selected detonation site. Additional oxidant may then be positionedin the enlarged borehole portion surrounding the detonation site andupwardly in the borehole to chamber dimensions. Easily decomposedoxidant could be placed in the borehole to a height corresponding to theexpected chimney dimensions to provide a late time oxidizing effect onchimney gases. Other procedures can be used to position the oxidant insurrounding relation to the explosive. For example, a dense aqueousslurry or suspension using, e.g., bentonite suspension agents could bepositioned in a manner similar to that used in concreting or grouting ofwell casing, e.g., by perforating the casing and pumping the slurry orsuspension outwardly into pores and fractures in the formation. Fluidand/or gaseous oxidants could be emplaced in a similar manner. Followingemplacement of the oxidant the borehole is stemmed and sealed in anyappropriate manner, e.g., as in the Gasbuggy" and Rulison experiments.(c.f. pp. 597 of said Proceedings") The amount of oxidant which is usedshould be sufficient to combine with all reducing materials in at leastthe emplacement components as well as in the melt zone expected to beproduced by the detonation. It is preferred that there be employed anexcess sufficient to assure that substantially no free hydrogen gas,i.e., H HT, -etc., remains in the gaseous atmosphere in the cavity andchimney. The amount of oxidant required may accordingly be determined asthat required on stoichiometric principles to oxidize all reducingmaterials in the melt zone which may be considered to include allportions of the formation heated sufficiently to ignite the reductants.To assure complete oxidation and therefore avoid formation of anyvolatile hydrogen containing products, other than possibly a smallamount of tritiated water vapor, an excess of oxidants may be used.Residual water vapor can be removed by dehydration procedures asdescribed above to further lower the tritiated water from the gaswithdrawn from the detonation chamber and chimney.

As reported in a paper entitled Interpreting the Chemical Results ofGasbuggy Experiment" by R. W. Taylor et al, page 794 of saidProceedings, the principal reactions which occur when a nuclearexplosive is detonated in a typical carbonate petroliferous formation,i.e., the Lewis shale are as follows:

2. C C0, 2 CO A Cori-H,

It may be noted that in the Gasbuggy environment the reactions aregenerally reducing in nature with carbon almost exclusively serving asthe primary reducing agent. From the Gasbuggy data reaction (1) appearsto be the main reaction. Several of the reactions lead to theincorporation of hydrogen into gaseous hydrocarbons (CH Tritium presentin the melted zone reaction environment accordingly is incorporated bysuch chemical reactions and by exchange reactions into tritiatedhydrocarbons .which contaminate hydrocarbon products withdrawn from thereservoir.

For the purposes of the present invention the reducing agents which maybe present will include carbon usually in a graphitic or amorphous form,lower aliphatic hydrocarbons such as CH C,H CaHg, C H etc., solidhydrocarbons, e.g., asphalts, paraffins, tars and other hydrocarbons oflesser proportionate hydrogen content than the paraffinic components andpossibly containing sulfur and nitrogen. Metallic iron, hydrocarboncomponents, etc., of nuclear explosive emplacement components will alsoact as reducing agents under the conditions herein. With an oxidantpresent it is desired that the following type reactions be drivensubstantially to completion.

u: man/2) m) z um d. Fe +0 FeO (some Fe=O possibly) e. (sulfides)+0,(sulfates) Under the indicated conditions reduction reactions of thetype indicated above which can yield gaseous hydrogen containing HT arenearly eliminated. It will be noted that CO formation and the formationof hydrocarbons by reactions occurring in the detonation chamber arealso minimized or eliminated during the explosion and high temperaturecooling time periods. The tritium formed or released in the explosion isalmost completely converted to tritiated water (HTO) dispersed in a verydilute admixture within vapor and/or condensed water phase. Asubstantial portion of the water eventually may combine with fusedsilicate and calcined carbonate rock, dolomite, calcite, etc., presentin the explosion chamber and thereby the tritiated compounds may beimmobilized to diminish the possibility of exchange reactions whichcould produce tritiated hydrocarbons with fluid or gaseous hydrocarbonswithdrawn from the formation through the detonation chamber as describedabove.

Various oxidizing agents may be employed for the purposes of theinvention. In the equations above, oxygen is shown as an illustrativeexample and may be used as high pressure gas pumped into the formation,if porous liquid oxygen, disposed in a cryogenic container might also beused to dispose at least a portion of the required oxidant in the wellbore. However, it is generally preferred to utilize a solid oxidant suchas manganese dioxide, sodium or potassium permanganate, alkaline earthor alkali metal chlorate, perchlorate, sulfate, nitrate, or othersuitable nitrate compound, sodium perborate or sodium peroxide,

which may conveniently be packed in the enlarged emplacement area aswell as in adjacent well-bore or emplacement drift regions. Similarlyfluidized, slurry or solution forms of the indicated oxidants may alsobe used, e.g., to facilitate injection into the formation proximate thedetonation site. The latter may comprise aqueous solutions, slurries offinely-divided oxidant or an aqueous suspension of the oxidant which maybe introduced into the formation using equipment of the type used forhydro-fracturing, or otherwise treating formations as commonly practicedin the art.

The amount of oxidant required may be calculated by analyticallydetermining the content of reductants present in the formation. Incertain petroliferous formations the carbon and hydrocarbon content mayrepresent the reductants of major importance. Under other conditions,especially where hydrocarbon content is low such as formations ofdolomite and calcite, ferrous sulfide may represent a major reductant.In the event iron is present in a hydrocarbon bearing formation, it willbe found that the ratio of Fe to Fe states will tend to be high.Sulfides, e.g., FeS may also serve as reductants. Total iron content inpetroliferous formations and other formations in which nuclearexplosives may be used may range up to wt or more. Metallic iron,organic compounds and organic compositions used in emplacementcomponents, canister and nuclear explosive device should also be takeninto consideration and the amounts thereof should be minimized to loweroxidant requirements.

The technique of the invention may generally be employed in anyenvironment wherein reductant materials are in stoichiometric excessover potential oxidizing components so that hydrogen forming reactionscan occur on detonation. For example, the formation may contain carbonabove 0.1 percent and/or similar amounts of hydrocarbon or other organicmaterial therein. It will be appreciated that the present techniquecould, in theory, be utilized with large proportions of reductants inthe formation and/or emplacement components. However, a practicaleconomic limit of about 5 to 10 wt of reductants may be imposed due tothe amount of oxidant that would be required. Some decrease in thecalculated quantity of oxidant required may be possible in the eventthat gaseous hydrocarbons are displaced outwardly in the formation byinjected oxidizing agents, the fluid used to inject the oxidizing agent,or by explosion produced gases. Moreover, zoning of the melted materialwithin additional material heated to a temperature high enough to burnthe carbon and other reductants may permit, for example, 500 to 700tons/kilotons of rock typically to be melted while the total heated tocombustion temperature may be of the order of 1100 to 1200 tons/kilotonexplosive yield including the melt zone. Dependent on the composition,water content and the like the amount of rock melted or otherwise heatedsufficiently by the nuclear detonation to heat and burn or oxidize thereductants may range from about 400 metric tons/kiloton explosiveequivalent to as high as about 1200 metric tons/kiloton (1 kiloton isequivalent to 10' calories) (See Proceedings pp. 794 reference ibid).

The amount of environmental reductant playing an active role inscavenging shot produced tritium may be limited by chemical reactionrate and/or heat and mass transfer rates. There may not be time for thechemical, physical, or thermal equilibration of tritium produced nearthe device with all the material heated by the detonation energy. Oftenthe hot cavity produced by the detonation is thermally quenched by therapid influx of colder materials occurring during cavity collapse. Uponcollapse volatile materials may escape into the cold chimney region andnot significantly interact thereafter with products from the hotmaterials near the detonation point. Thus the tritium emanating from thedetonation may react with (I) only the approximately 100 tons/kiloton ofrock vaporized by the shockwave from the detonation, (2) the roughly 300total tons/kiloton initially melted by the shockwave, (3) the 700 or sototal tons/kiloton melted when cold rock contacts the superheated shockmelted rock or (4) the 1000 or so total tons/kiloton eventually heatedsufficiently to react in situ free carbon with steam and carbon dioxide.

It is necessary that sufficient oxidant be provided to oxidize thereductants present in the melted rock, i.e., usuallyabout 500 to 1200metric tons/kiloton explosive equivalent as well asto account foremplacement components. Typically, the amount of molten rock producedmay range from about 500 to 1200 metric tons per kiloton of explosiveyield. Nuclear explosive yields in the range of l kiloton to 100kilotons may be employed. For many petroliferous formations nuclearexplosive yields in the range of about 5 to 100 kilotons are consideredsuitable with depths of burial ranging from about 2000 feet to about15,000 feet which provide for fully contained detonations and as may beselected to provide for the required rock breakage, cavity and chimneyvolume or extent of fracturing desired. The detonation size may also bedetermined by seismic limits as disclosed in the copending applicationof Milo D. Nordyke for Nuclear Explosive Method for StimulatingHydrocarbon Production from Petroliferous Formations filed Ser. No.89,889, Nov. 16, 1970.

When nuclear explosives are detonated in the presence of oxidants asdescribed a major proportion of the tritium, i.e., above percent of thatnormally expected to appear in gaseous or hydrocarbon form, will insteadbe in the form of HTO and such form will largely be entrapped in animmobilized form within the formation debris. Whatever tritiated watervapor occurs in admixture with normal water vapor in gaseoushydrocarbons withdrawn from the cavity formed by the detonation can beremoved therefrom by a conventional gas drying operation at the surfaceor by other techniques well known in the prior art.

Further details concerning operation of the technique of the inventionwill be apparent in the following illustrative example:

EXAMPLE lnformation relating to the composition of a typical shale zone,the "Lewis" shale, in which a nuclear explosive has been detonated,i.e., the Gasbuggy" operation, and various other parameters and detailsrelating to such a typical operation are set forth in a paper entitledInterpreting the Chemical Results of the Gasbuggy Experimentpp. 794, etseq., of said Proceedings" and references cited therein. Otherinformation is set forth in Gasbuggy Preshot Summary Report (PNE-lOOl,1967) U. S. Atomic Energy Commission.

EXAMPLE 1 The Gasbuggy Situation This example presents a calculation inwhich a nuclear detonation is fired in a relatively reductant richenvironment. The conditions given are actual data derived from theGasbuggy experiment.

TABLE 1 Parameters of the Gasbuggy Experiment pertinent to presenttechnique:

Dcvicc Yield Cavity Radius Rock Heated to Reactive Temperatures (l 100tons/kiloton) Reactive Materials in Rock (Lewis Shale) Free Carbon (0.5wt FeS (0.8 wt 5) Fe,0 (3 wt R (1 wt Hydrocarbons (0 wt 12) 26 kilotons80 ft 28,600 metric tons 143 metric tons 228 metric tons 858 metric tons286 metric tons 0 metric tons Reactive Materials in Emplacement HoleCavity Region Table 2 indicates the relative oxidizibility of theelements sulfur, iron, carbon and hydrogen over the range oftemperatures encountered at late times in nuclear cavities. The leaststable oxides are at the top of the table. Before a given oxide can beformed, sufficient oxidizer must be provided to form the oxides below itin Table 2. For the purpose of reducing undesirable tritium compounds weshall provide enough oxidizer to form C0, and FeO which prevents thefollowing reactions from occurring:

Further oxidizer could be added to produce the reaction H,S 0, H 0 SO,which would prevent escape of HTS in the product gas. However in thisexample we shall assume any tritiated H,S can be removed from theproduct stream by conventional methods.

In the particular example of Gasbuggy, the ferric oxide in the rock willact as an oxidizer, liberating oxygen by thermal decompositon accordingto the reaction In fact the oxygen derived from ferric oxide is morethan enough to oxidize the iron in the device plus the iron liberatedfrom iron sulfide to ferrous sulfide.

Thus in the Gasbuggy case to produce a sufficiently oxidizingenvironment enough oxidizer should be added (with 10 percent excess) tooxidize 143 tons of free carbon to carbon dioxide and 12 tons of iron toferrous oxide.

To oxidize the carbon, 420 tons of oxygen is required, which mighttypically be supplied in the form of 1500 tons of manganese dioxide ore,assaying MnO An additional 25 tons of ore would be required to oxidizethe iron.

This ore could be put in the device emplacement hole from one cavityradius above to one cavity radius below the device. The emplacement holewould have to be underreamed to a 12 foot [.D. in the cavity region.Alternatively the ore could be forced into rock fractures with a fluidas described above or a fluid oxidizer could be used.

Note that the foregoing indicates a maximum amount of oxidant additiverequired. If the melt is nearer 500 tons/kiloton than 1000 tons/kiloton(as is entirely possible) only about one-half as much oxidant would berequired.

EXAMPLE 2 Carbonate Rocks This example'presents a'calculation for adetonation in a low reductant environment. Many petroliferous formationsin-the Southwest United States are adjacent to relatively pure, thickstrata of dolomite [Mg Ca (CO or calcite (CaCO )..The only majorreductants affecting a detonation in this media are the emplacementhole'casing (if any), the device canister and insulation on electricalcables.

Again consider the Gasbuggy device (26 kilotons) detonated in a casedhole in a carbonate media at a depth of about 5000 feet. At this depth,the total cost of the emplacement hole plus device is about the same foremplacement hole diameters in the range 14 to 24 inches ID. (F. E. Hill,pp 68 in Symposium on Engineering with Nuclear Explosives). Assume forthis example a 24 inch lD casing 3/4 inch thick weighing about 0.1tons/ft of iron and extending to one cavity radius below the shot point.The device contains about 1 ton of iron. The total weight of iron in afoot radius cavity will be 17 tons. The plastic and paraffin in thecavity region will be at most /5 ton.

About two tons of MnO, ore per ton of iron and 25 tons of MnO, ore perton of plastic are required for complete oxidation to FeO, CO, and H 0.With a 10 percent excess about 50 tons of MnO, ore are required. Thisamount of etc could be placed in 180 feet of emplacement hole. Thus theoxidant would all be near the molten rock in the cavity with nounderreaming required.

If Mn0, were placed in an uncased 24 inch hole below the shot point,only feet of Mn0, would be required to produce an oxidizing atmosphere.

If no hole casing were required in the cavity region and chemicallyinert electrical insulation were used.

The amount of Mn0, ore required would drop to about 3 tons. The 3 tonscould be held in less than ll feet of 24 inch lD emplacement hole. Inthis case no extension of the emplacement hole below the detonationpoint would be required.

While there has beendescribed in the foregoing what may be considered tobe preferred embodiments of the invention, modifications may be madetherein without departing from the concepts of the invention, and it isintended to cover all such as fall within the scope of the appendedclaims.

What we claim is:

l. A process for decreasing radioactive contamination of the atmospherein a cavity and chimney formed by detonation of a nuclear explosive in asubterranean formation which contains an excess of chemical reductantmaterials therein comprising:

a. providing passageway means from the surface extending to saidformation, said passageway terminating in an emplacement cavity withinsaid formation;

emplacing a fission-fusion nuclear explosive device within said cavity;

c. disposing a quantity of oxidant circumjacent said nuclear explosivedevice sufficient to oxidize the chemical reductant materials as well asreduced state radioactive contaminants formed in the detonation;

d. stemming said passageway; and

e. dctonating said nuclear explosive device so that said oxidantprovides an oxidizing environment in the vicinity of the detonateddevice adequate to oxidize volatile radioactive compounds and precursorsof radioactive compounds including tritium created by the detonation toform nonvolatile or condensible products therewith to minimizeradioactive content of the atmosphere in the cavity and rubble chamberproduced by the detonation.

2. A process as defined in claim 1 wherein said subterranean formationis a hydrocarbon bearing formation also in which said materials includematerials selected from the group consisting of carbon, hydrogendeficient carbon compounds, metallic sulfides and metallic iron.

3. A process as defined in claim 2 wherein said oxidant is a materialselected from the group consisting of oxygen, manganese dioxide, alkaliand alkaline earth metal chlorates, perchlorates and nitrates, sulfates,sodium perborate and sodium peroxide.

4. A process as defined in claim 3 wherein components having reductantproperties are used in emplacing said nuclear explosive device andwherein sufficient additional oxidant is emplaced in the vicinitythereof to oxidatively react therewith.

5. A process as defined in claim 3 wherein said subterranean formationis a natural gas bearing formation, wherein said natural gas enters therubble chamber formed by said detonation, said gas having a decreasedcontent of tritium and tritiated gaseous hydrocarbon compounds due tooxidation of the tritium by said oxidant, and wherein natural gashydrocarbon is withdrawn from said rubble chamber to the surface for useand distribution.

6. A process as defined 1n clalm 5 wherein the emplacement cavity insaid formation is disposed in a formation stratum in close proximity togaseous hydrocarbon bearing strata from which production is desired,said stratum having a low content of reductants therein wherefor theamount of oxidant required is decreased, and wherein the rubble chamberproduced by the detonation interconnects as by means of formationfractures with the hydrocarbon bearing formation.

7. A process as defined in claim 6 wherein the quantity of oxidant isdetermined with reference to the reductant content of the melted zoneformed by the detonation.

1. A process for decreasing radioactive contamination of the atmospherein a cavity and chimney formed by detonation of a nuclear explosive in asubterranean formation whiCh contains an excess of chemical reductantmaterials therein comprising: a. providing passageway means from thesurface extending to said formation, said passageway terminating in anemplacement cavity within said formation; b. emplacing a fission-fusionnuclear explosive device within said cavity; c. disposing a quantity ofoxidant circumjacent said nuclear explosive device sufficient to oxidizethe chemical reductant materials as well as reduced state radioactivecontaminants formed in the detonation; d. stemming said passageway; ande. detonating said nuclear explosive device so that said oxidantprovides an oxidizing environment in the vicinity of the detonateddevice adequate to oxidize volatile radioactive compounds and precursorsof radioactive compounds including tritium created by the detonation toform nonvolatile or condensible products therewith to minimizeradioactive content of the atmosphere in the cavity and rubble chamberproduced by the detonation.
 2. A process as defined in claim 1 whereinsaid subterranean formation is a hydrocarbon formation also in whichsaid materials include materials selected from the group consisting ofcarbon, hydrogen deficient carbon compounds, metallic sulfides andmetallic iron.
 3. A process as defined in claim 2 wherein said oxidantis a material selected from the group consisting of oxygen, manganesedioxide, alkali and alkaline earth metal chlorates, perchlorates andnitrates, sulfates, sodium perborate and sodium peroxide.
 4. A processas defined in claim 3 wherein components having reductant properties areused in emplacing said nuclear explosive device and wherein sufficientadditional oxidant is emplaced in the vicinity thereof to oxidativelyreact therewith.
 5. A process as defined in claim 3 wherein saidsubterranean formation is a natural gas bearing formation, wherein saidnatural gas enters the rubble chamber formed by said detonation, saidgas having a decreased content of tritium and tritiated gaseous hydrocarbon compounds due to oxidation of the tritium by said oxidant, andwherein natural gas hydrocarbon is withdrawn from said rubble chamber tothe surface for use and distribution.
 6. A process as defined in claim 5wherein the emplacement cavity in said formation is disposed in aformation stratum in close proximity to gaseous hydrocarbon bearingstrata from which production is desired, said stratum having a lowcontent of reductants therein wherefor the amount of oxidant required isdecreased, and wherein the rubble chamber produced by the detonationinterconnects as by means of formation fractures with the hydrocarbonbearing formation.